Transportation means

ABSTRACT

Means of transportation comprises a vehicle movable along a track having a branching zone and at least two alternative branching routes with guidance means in the form of a stationary guide member associated with each said route. A vehicle-mounted follower is engageable with one of said guide members to cause the vehicle to move along one branching route and a second selectively operable vehicle-mounted follower is engageable with the other guide member to cause disengagement of the first follower as a result of transverse movement of the vehicle which thus travels along the other branching route. The propulsion means for the vehicle may include a magnetic member mounted on the vehicle and a stationary magnetic member extending parallel to one side of the branching zone.

United States Patent [191 Perrott Mar. 18, 1975 TRANSPORTATION MEANS[22] Filed: Oct. 30, 1973 [21] Appl. No.: 411,060

Related U.S. Application Data [60] Division of Ser. No. 190,627, Oct.19, 1971, Pat. No. 3,777,667, which is a continuation of Ser. No.779,977, Nov. 29, 1968, abandoned.

[30] Foreign Application Priority Data Aug. 21, 1968 [56] ReferencesCited UNITED STATES PATENTS Hawes 104/130 United Kingdom 3983/68,

3,500,765 7/1970 Easton et a1. 104/130 Primary Examiner-James B. MarbertAssistant ExaminerRobert Saifer Attorney, Agent, or FirmYoung & Thompson[57] ABSTRACT Means of transportation comprises a vehicle movable alonga track having a branching zone and at least two alternative branchingroutes withguidance means in the form ofa stationary guide memberassociated-with each said route. A vehicle-mounted follower isengageable with one of said guide members to cause the vehicle to movealong one branching route and a second selectively operablevehicle-mounted follower is engageable with the other guide member tocause disengagement of the first follower as a result of transversemovement of the vehicle which thus travels along the other branchingroute. The propulsion means for the vehicle may include a magneticmember mounted on the vehicle and a stationary magnetic member extendingparallel to one side of the branching zone.

2 Claims, 18 Drawing Figures- PATENTED' 1 W75 Hall Hall

sum 3 OF 6 FIG/Z.

PATH-mu 1 3 87 1,300

PATENTEB 1 8 7 SHEET 6 6 ALL- TRANSPORTATION MEANS.

RELATED APPLICATIONS This application is a division of co-pendingapplication Ser. No. 190,627, filed 19 Oct., 19-71 as a continuation ofapplication Ser. No. 779,977, filed 29 Nov., 1968, No. 779,977 is nowabandoned; while No. 190,627 issued to US. Pat. No. 3,777,667 on Dec.11, 1973.

FIELD OF THE INVENTION This invention relates to transportation meanscomprising a vehicle movable along a track having a selective branchingzone and at least two alternative branch.- ing routes. Two alternativeguidance means for the vehicle are provided, each guidance meanscomprising a stationary guide member extending substantiallycontinuously along the track through the branching zone.

It is an object of the invention to provide improvements in suchtransportation means. In particular it is an object of the invention toprovide such transportation means which includes primary and secondaryvehiole-mounted followers associated with and engageable with guidesurfaces of saidguidance means. A further object of the invention is toprovide such a transportation means wherein magnetic propulsion means isprovided.

SUMMARY OF THE INVENTION A vehicle-mounted secondary follower isoptionally engageable from above with and is associated with anoutwardly facing guide surface with the arrangement such that when suchengagement takes place the primary follower disengages from its guidesurface. Such disengagement occurs solely as a result of the transversemovement of the vehicle. The track may be inclined transversely wherebythe vehicle is transversely loaded to maintain effective contact with aselected one of the guide surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a somewhat diagrammatic endview of a vehicle and associated track guidance means in accordance withone embodiment,

FIG. 2 is a corresponding track plan view,

' FIG. 3 is a view generally similar to that'of FIG. 1, but of anotherembodiment,

FIG. 4 is a similar view of a further embodiment,

FIG. 5 is a fragment of FIG. 4 illustrating one guidance condition,

FIG. 6 is again a similar view of yet another embodiment,

FIG. 7 is again a similar view of a yet further embodiment,

FIG. 8 is a similar view of an embodiment utilising a linear inductionmotor for propulsion,

FIG. 9 is a lateral sectional view of another embodiment.

FIG. 10 is a fragment of the view of FIG. 9, showing an alternativeguidance condition,

FIGS. 11 to 13 illustrate track forms for the embodiment of FIGS. 9 and10,

FIGS. 14 to 16 are lateral sectional views of alternative air cushionbearings for use to support a vehicle according to the invention,

FIG. '17 is a lateral sectional view of yet another embodiment, and

FIG. 18 is a plan view of'the embodiment of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiment of FIG. 1 thevehicle 1 is supported by means such as a fluid cushion 2 on a singleplane track surface 3. Alternatively, dual trackways may be provided forsupport wheels (not shown), and propulsion may. be by any suitablemeans, such as wheels, linear induction, or airscrew. For simplicity,means of propulsion are not shown in FIG. 1. Guidance is normally by aside-rail 4, which is engaged by a follower arm member 5 mounted on thevehicle 1 In some cases the follower arm 5 may control vehicle steeringmechanism and, in such cases, a single set of follower equipment, as isbeing described, will suffice. In other cases, the vehicle is directlylocated in the transverse direction by the follower equipment and forthis purpose the equipment illustrated is duplicated in a transversesection which is removed from the present one. In such cases, motion ofthe two follower arms 5 Referring to the track plan of FIG. 2, which ison a smaller scale than FIG. 1, the vehicles travel from the bottomtowards the top of the drawing. A vehicle programmed to travel straighton at thejunction X continues guided by the lefthand guide rail 4. Thetrackside transmitter 8 transmits to the vehicle a simple and ordinarysignal in a manner well known, such as by a trip lever, a magnet, or abeam. Upon passing this transmitter, a vehicle-mounted programming unit(not shown) receives this signal and is advanced one step. Such aprogramming unit may comprise any of those well known in the railroadart, for example, a ticket in the form of a route card, each step ofwhich contains a specific vehicle command either to branch left .or tobranch right.

If the vehicle is already programmed to branch right, it still uses thelefthand guide rail 4 for its approach and the trackside transmitter 8again advances the programming unit one step. However, in this case theprogramming unit 8 causes the follower arm 7 to engage the guide rail 6,and subsequently the follower arm 5 is disengaged fromthe guide rail 4.The lower break in the FIG. 2 drawing signifies a substantial distance,so

that these operations are completed before the branch junction X isreached. The vehicle is then guided to the right, by the guide rail 6,and it continues to be so guided, for the substantial distance which isrepresented by the upper break in the drawing. Subsequently, a furthertrackside transmitter 9 advances the programming unit by another step,causing the vehicle to change back to the lefthand guide rail 4. Inorder to illustrate the advantages of this system, its logicalderivation from existing road transportation will now be outlined.

The main advantage of road transportation is individual route selection.By this is meant, the ability of each individual vehicle to choose whichway it goes when the road branches. By a succession of such choices, itfollows its own selected route, to a specific destination. In order toobtain this advantage, vehicles are given complete freedom of steering,at all times. Amongst the infinite range of choice which is thusprovided, the driver has continuously to select the required path.Steering is truly of use only when the vehicle is actually choosingbetween alternative road branches and all other degrees of freedom ofsteering are, from the fundamental viewpoint, not only redundant butactually harmful.

The feature of the present invention which has been described withparticular reference to FIGS. 1 and 2 is referred to, in principle, astrack selection.

Track selection retains the essential freedom of route selection but, atother times, the vehicle is guided by the track, like a railway train.The track or tracks need be no wider than is required to support thevehicle wheels or other support means employed. Rigorous speed controlmay be imposed, and safeguarded by au tomation. This decreases thecapital cost of track construction and, indirectly, increases itscarrying capacity.

An initial application for transportation means according to theinvention could be between two points, such as an airport and a citycentre. In such a case, automatic terminal control might guide thevehicles into appropriate loop sidings, with automatic approach controlfitting the vehicles between one another, at track junctions, as theyleave the loop sidings. Speed control would prevent collisions betweenvehicles which are moving behind one another, on the same track.

At a second stage of development, a plurality of terminals could beserved by the same main line. Each vehicle would then be programmed inadvance, to select the correct sequence of lefthand and righthandbranches in the track. For example, a sequence such as "left, left,right, right, left, would cause the vehicle to branch left at the firstbranch of the track, corresponding to the first step in its programmingunit or ticket, left at the second branch, corresponding to the secondstep in the vehicle-mounted programming unit described above, and so on.By this means alone, each vehicle would be directed to its prescribeddestination.

These developments, and those which are about to be described withparticular reference to the remaining drawings, all tend to increase thetrack carrying capacity, both relative to the area occupied and the lossof urban amenity, and also in relation to the capital cost of trackconstruction. The ultimate level of carrying capacity, of a singletrack, is very high, and thus it is economic to sacrifice some of thispotential capacity in order to reduce vehicle unit size, with consequentadvantages relating to the maintenance of urban amenity and cost oftrack construction.

In order to illustrate the additional advantages which result fromfurther development, the logical derivation of this system from existingrail transportation will now be outlined. The main advantage of railtransportation is carrying capacity, both relative to the space occupiedby the track and to the cost of track construction. The maindisadvantage is that it has to use large trains, between large terminalsand/or intermediate stations, i.e. there is a lack of route choiceflexibility. The carrying capacity is obtained by vehicle guidance.However, this capacity is restricted by the need for block control,which necessitates large stretches of unused track, be-

tween each section which is actually in use, beneath the wheels of apassing train. In order to minimise this waste of space, long trains areused, thereby increasing the ratio of track used to track wasted. Longtrains impose the ultimate limit on carrying capacity, by theirrequirement for terminal facilities, they also destroy the route choiceflexilibity which is an important passenger requirement.

By transferring the route-selection faculty from a trackside signal boxto each individual vehicle concerned, track selection goes a long waytowards eliminating the need for block control. It is proposed tocomplete this elimination, in a system of transportation according tothe present invention, by the use of automation in conjunction withimproved vehicle braking. Not only does this enable vehicles to runcloser together, but it eases the terminal bottleneck. This is becausevehicles which are travelling close behind one another can be directedinto separate loop sidings, which are off the main track. Thus aplurality of smaller and more conveniently situated terminals becomesavailable. In terms of long-term development potential, the number ofsecondary tracks which feed a main line increases. As main line trafficdensity progressively increases, the air is to form groups ofindependent vehicles which maintain light end-to-end contact with oneanother. Vehicle mounted automatic speed control is provided, to causevehicles running close together to establish this end-to-end contactwithout shock. In order to avoid instability, and to minimise the numberof trains so formed, speed control preferably either always speeds up afollowing vehicle, to contact the one in front, or vice versa. Suchtrains can be longer than customary railway trains, because they escapethe limits imposed by starting and stopping facilities. At branches theyseparate out, and proceed to their separate destinations. Provided thatgaps so formed are reasonably small, they are subsequently automaticallyclosed up again.

A secondary advantage which results from forming groups in the foregoingmanner is that it eliminates the problems associated with collectivestability between vehicles running close together, but not in contact.The limit to a main line carrying capacity is no longer terminalfacilities, together with train length, but the acceptable waiting timewhile one train is waiting to enter a section of main line, behind aprevious one which is passing. While a train is waiting, other vehiclesmay arrive at the rear and establish contact with it. At the right time,they are started by computer, so as to follow the train which has justpassed. By the elimination of block control and by the use of longtrains of vehicles in light end-to-end contact, the ultimate limit ofcarrying capacity is very high indeed. The following description appliesto a design study proposing a system utilising very light individualvehicles.

The proposed system will carry in the order of 20 times as manypassengers per hour as a double threelane motorway, yet its track isonly one sixth of the corresponding width while only one half of thecorresponding clearance height above the track is required. Small andlight driverless vehicles are individually programmed in advance, sothat each follows its own independent route, even over the most complextrack network, without the need to reduce speed. Urban terminals aresituated actually inside the larger buildings, in order to reduce rushhour street congestion, and suburban terminals are adjacent car parkschosen for road access.

Various alternative embodiments of the track selection principle willnow be described. In respect of features not individually specified,those generally resemble those already described with particularreference to FIGS. 1 and 2.

FIG. 3 of the drawings illustrates a transverse section through avehicle designed for factory goods distribution, which is a possibleinitial application with low development costs. The vehicles is in theform of a truck which runs on wheels 12 over factory floor 13. It isguided either by a follower member 14 engaging a floor slot 15, asshown, or by a follower l6 engaging a floor slot 17. A programming unitselects the appropriate channel follower 14 or 16 at each branch orjunction, to route the truck to its required destination.

FIGS. 4 and 5 illustrate one application of the invention to theWestinghouse so-called transit express way. The vehicle 18 is supportedon double pneumatic-tired wheels 19 which run on spaced track members 20and 21. Transverse guidance is provided by two horizontal wheels 22 and23 with vertical axes of rotation, which engage channel members 24 and25 beneath the top webs 26 of which the wheels 22 and 23 engage with akeying effect in order to prevent all possibility of the vehicleoverturning. In the existing system the track is without branches, orjunctions, in the normal sense and the wheels 22 and 23 engage a singlecentral channel member below the vehicle thus if it is desired to movethe vehicle 18 on to another track it is stopped on a section of trackwhich is slidable transversely and the vehicle and track section movedbodily to realign with the second track. This is inconvenient foroperation at high traffic densities, because the main line is out ofaction while a vehicle is being transferred.

The application of track selection to this system is illustrated in FIG.4 which represents thecondition for all occasions except branches to theright and junctions from the right. The use of outwardly spaced guidemembers 24 and 25 above the track members 20 and 21 results in muchincreased stability as well as providing for track selection, andsupplementary vehiclemounted horizontal guide wheels 27 and 28 can beraised or lowered along their vertical axes. The wheel 27 is shownlowered in FIG. 4, to engage a vertical track side face 29 which, inthis case, is provided by a filling piece 30 in the corresponding maintrack member 20. A similar filling piece 32 in the other track member 21provides a side face 33.

At a track branch the members 24 and 25 separate, the vehicle 18 beingguided by wheels 22 and 27, with the wheel 23 temporarily disengagingthe side member 25. FIG. 5 shows the corresponding operating positionfor right-hand branches, or for junctions from the right. The wheel 27is raised, and the wheel 28 is lowered. When the members 24 and 25separate, the wheel 22 is temporarily disengaged from the member 24 andthe vehicle 18 is guided by the wheels 23 and 28.

In FIG. 6 there is illustrated the application of the invention to theBrush Electrical so-called automatic self-routing taxi system. Thevehicle is supported on pneumatic-tyred wheels 41 which run inside asingle channel-shaped track 42, as compared with the spaced twin tracksof the existing proposal in which automobile-type steering is providedand controlled by an electric pick-up arm which engages an overheadguide track. On approaching a branch, this pick-up arm is given a biasto whichever side of the branch the vehicle is to follow and there isthe considerable disadvantage that the arm is affected by vehiclerolling motion, and thus the system has limited margins of robustness,stability and safety.

In the present application of track selection, additional horizontalwheels 43 and 44 follow surfaces of curb members 45 and 46 which areperpendicular to main track surface and in effect form side webs of thetrack member 42. These wheels 43 and 44 may be preloaded in order tomaintain contact at all times, with one or other wheel used forsteering.

According to one construction, the steering wheel is linked toservo-mechanism, which governs the vehicle steering. Saidservo-mechanism maintains a nominal datum position of the vertical axisof rotation of the wheel 43 or 44 concerned, relative to the vehicle 40.

According to another construction, the wheels 43 and 44 are connectedwith servo-mechanism which operates to maintain pressure with whichevercurb member 45 or 46 is being used for guidance.

According to yet another construction, the servomechanism is omitted,and the vehicle steers to maintain pressure with the appropriate curbmembers 45 or 46, and such pressure is limited by vehicle steeringcharacteristics, e.g. castor action, or by placing horizontal wheels infront of the vehicle wheels carrying the weight, so that contact withthe curb produces a correcting couple. The curb members 45 and 46temporarily separate at branches and junctions, and the vehicle is thenguided by the lefthand curb member 45, for lefthand branches andjunctions, and by the righthand curb member 46 for righthand branchesand junctions.

An embodiment of the invention with certain advantages, especially foroutdoor vehicular transportation, is illustrated in FIG. 7. The vehicle50 runs on pneumatic-tyred road wheels 51 and 52 over plane surfacedtracks 53 and 54, the surfaces 55 and 56 of which lie on the sametransverse straight line and are inclined to the horizontal. The axis ofrotation of the wheels 51 and 52 is parallel to the main track surfaces55 and 56. FIG. 7 represents conditions for lefthand branches andjunctions and between branches and junctions. A vehicle-mounted wheel 57has an axis of rotation which is perpendicular to main track surfaces,and it engages a perpendicular track guide surface 58 on a side guidemember 59.

A further vehicle-mounted guide wheel 60 has an axis of rotationperpendicular to the main track surfaces, and it can be lowered alongits axis of rotation to engage a perpendicular guide'surface 61 formedon the track member 54. This is the position for righthand branches andjunctions from the right, and the wheel 57,tempora rily disengages fromthe guide track surface 58 under those conditions. It will be noted thatthere is no mean side-thrust on the wheels 51 and 52, because any suchthrust would result in transverse lift of the veupon the vehicle 50,which locates it transversely against side guide track surface 58. Thusthe need for a second similar surface on the other side is eliminated.Another advantage is that stones, snow and the like slide off the track,and it is less likely that pedestrians will walk upon it. It alsoprovides the opportunity to en sure fail-safevehicle removal to theleft, at any branch.

FIG. 8 illustrates the application of track-selection to a vehicle 70 ofthe type known as a tracked Hovercraft, with propulsion by linearinduction. A corresponding form would suit the Bertin so-calledaerotrain. The vehicle 70 rides on air cushions 71 and 72 above atrackway 73 the upper track surface 74 of which is inclined to thehorizontal at about for the same reasons as with the wheeled embodimentof FIG. 7. The drawing shows conditions for lefthand branches andjunctions. Transverse location is provided by a vehicle located aircushion member 75 which slides on a side guide track 76 the guidesurface 77 of which is generally perpendicular to the main track surface74. An alternative vehicle-mounted air cushion member 78 is providedwith means for lowering, to engage the per pendicular track side guidesurface 79, and it is so lowered for righthand branches and junctionswhen the cushion member 75 is temporarily disengaged from the guidetrack 76. Conductor strips 80 and 81 are provided for propulsion bylinear induction, and they are parallel to the main track surface 74 andeach suitably supported at its outer extremity. At branches andjunctions, the distance between the conductor strips 80 and 81 istemporarily increased and the vehicle is then propelled, as appropriate,by only one strip with the other strip sliding transversely from the gapbetween the magnets concerned. This avoids the need for articulatedmagnets for linear induction.

The embodiment shown in FIGS. 9 and 10 is a development of that of FIG.8 which is especially suitable for fluid cushion slipper bearingsdesigned to operate at higher pressures than are usually employed forHovercraft. It is also suitable for use where the slipper bearings,which are described by way of example, are replaced by wheels. Increasedslipper bearing pressures reduces the track surface width requirementand economic and aesthetic considerations then demand use of a reducedtrack width. The reduced track width tends adversely to affect rollingstability, and according to this embodiment the side guide track member90 is removed from main track surface 91 by a transverse distancesufficient to provide a satisfactory lever arm for adequate rollingstability. It is provided with one or two slipway surfaces suitablyangled to ensure rolling stabilty, i.e. with a component of area whichis sufficient for the purpose and perpendicular to the local directionof motion in rolling.

The body of the vehicle 92 is a circular member, and the weight iscarried by the inclined resin-faced slipway surface 91 on afactory-produced and prestressed concrete beam member 93. The side trackmember 90 provides a slipway surface 94 perpendicular to main slipwaysurface 91 and engageable by a fluid cushion slipper bearing 95. It alsocomprises opposed slipway surfaces 96 and 97 parallel to the mainslipway surface, and engageable by fluid cushion slipper bearings 98 and99 which provide rolling stability while the bearing 95 providestransverse location. Duplicated equipment,

similar to that just described, provides stability in respect of yawingabout a vertical axis.

FIG. 9 shows the condition between junctions and branches, and forlefthand branches and junctions. The slipper bearing is pre-loaded by acomponent of reaction from the main slipway surface 91 which is engagedby the vehicle support slipper 100 and acts to the left. Propulsion isby linear induction, utilising vehiclemounted electromagnets 101 and102, which are energised through track-mounted conductor strips, 103,104 and 105. Suitable vehicle-mounted electrical pick-ups are provided,as shown diagrammatically at 106, and the propulsion conductor strip 107is parallel to main slipway surface 91. An additional fluid cushionslipper bearing 108 is provided, with means for rotation about an axis109, and is shown in the raised position.

The conditions for righthand branches and junctions are shown in FIG.10. The fluid cushion slipper bearing 108 is lowered to engage the sideslipway surface 110, which is perpendicular to the main slipway surface91, and to the direction in which slipper bearing 108 is movable.Vehicle transverse location is then by the slipper bearing 108 opposedby a transverse component of reaction form the main slipway surface 91.A second linear induction conductor strip 111 is engaged, and this isalso parallel to the main slipway surface 91. Electromagnets for linearinduction are duplicated at 112 and 113, as are the conductor strips andassociated electrical pickups. Rolling stability is still provided bythe righthand side track 114, through slipper bearings 115 and 116 whichact upon opposed slipway surfaces 117 and 118, again both parallel tothe main surface 91.

At junctions and branches the two side tracks 90 and 114, together withthe linear induction equipment, are separated, in the same way asalready described for the embodiment of FIG. 8. Not only are the linearinduction strips 107 and 111 disengaged, without introducing articulatedparts, but the slipper bearings provided for stability in rolling, andfor transverse location, are similarly disengaged without articulation.The only articulated part is the subsidiary slipper bearing 108.

FIGS. 11 to 13 illustrate diagrammatically track forms suitably used.Referring particularly to FIG. 12, which is a lateral section through alength of an overhead twin-track system, the lefthand track member isinclined to the left as in FIGS. 9 and 10 and the transverse reaction isnormally sustained by the side guide member 90. The righthand trackmember 930 is oppositely inclined, i.e. to the right, and the transversereaction is sustained by the guide member 90a on that side. The completetrack is supported on columns 119, which allow for free normal trafficbelow the track.

The invention is also concerned with the provision of suitable fluidslipper bearings for a transportation vehicle. It has been proposed thatair from a pressure vessel should penetrate a porous resistor to producea stable air film over a compliant (elastomer) faced track.Disadvantages of this proposal are that the track requires a coating ofthe elastomer, which will normally be adversely affected by sunlight andcannot be repaired without putting the track completely out of action.In addition, the porous resistor tends to become blocked, because thepore passages must be small relative to the air film thickness in orderto ensure stable film and blockage ruptures the air film, with resultanttrack damage. For these reasons, it is preferable to transfer thecompliant function to the porous resistor itself. However, in its simpleform, this is wrong in principle as the pressure differential merelyforces the resistor against track surface, sealing it.

FIG. 14 shows a solution which is provided by the present invention.Air, in an enclosed space 120, penetrates metering holes 121 which areprovided in a rigid metering plate 122. Air then passes through lowresistance holes 123 in a compliant member 124 which is of a materialsuch as sponge rubber. Beneath the compliant member 124 there is adimpled semi-compliant facing member 125. This is of a material,preferably, which not only has the required stiffness characteristicsbut also has self-lubricating and bedding properties, such as purepolytetrafluoroethylene(P.T.F.E.). The passages 123 communicate with thedimples in the facing member 125, which dimples act as ordinaryaerostatic bearings to ensure a relatively thick and stable air film at126 between the slipper bearing and a relatively smooth slipway face127.

The compliance of the slipper bearing is sufficient to accommodate minorirregularities in the slipway surface 127 but it is at the same timesufficiently stiff to prevent air film rupture at positions between thedimples of the facing member 125. This property is important, both whencrossing irregularities in the track surface, and in the case of localzones of film instability which may be created by aerodynamic influence.

According to the invention, a slipper bearing such as that justdescribed may be provided with means for pivoting, so that it can act asan ordinary pivoting thrust bearing when its rubbing speed issufficient. According to another feature of the invention, such aslipper hearing is used to provide supplementary air film lubricationbeneath the primary seal of an air slipper bearing of the type now to bedescribed with particular reference to FIG. 15. It may help startingand/or supplement the hydrodynamic film locally.

FIG. 15 illustrates a type of fluid cushion slipper bearing which couldbe used as a vehicle suspension unit. A soft-backed, and P.T.F.E. faced,sealing ring 130 slides on a resin-faced concrete slipway member 131. Aload carrying member (for example a vehicle) 132 is supported on a fluidcushion at 133. The ring 131 provides a primary seal and leakage isprevented by a secondary sealing ring 134, which slides on the primarysealing ring 130 and has enough flexibility to accommodate slightovality, so that the primary seal can pivot, advance or retreat.

A continuous fluid film is provided beneath the primary seal, andpressure in this film graduates from that inside the seal to thatoutside. The film provides a net upward force on the primary seal whichis hydrostatically balanced by the full interior pressure acting uponthe interior surface of the facing ring of primary seal, in conjunctionwith the exterior pressure acting on outside of seal, and springs (notshown) are provided to ensure initial sealing.

Approximate operating conditions are as follows:

Cushion pressure, 7 psi.

Mean net loading of primary seal on slipway, 0.02 pm.

Mean clearance 135 beneath primary seal, 0.003. It is the clearance 135which may be stabilised by the use of the described featureincorporating the semiresilient and dimpled facing member 125.Experience with liquid bearings of this type has shown that, underfavorable conditions, a hydrodynamic wedge developes between the primaryseal and the slipway surface, so

that the fluid cushion becomes self-pressurising. A theoretical analysisis backed up by enough testing to show that it is possible to ensurethat the net pressure of the primary seal, upon the slipway, is of thelow order stated. This reduces the air film lubricating requirement.

FIG. 16 illustrates a developed form of fluid cushion support unit, inaccordance with the invention, which is generally circular about an axis140. At the bottom, a concrete track 141 comprises a resin-faced slipway142 upon which slides the specially balanced sealing ring assembly orprimary seal 143. The bottom of the vehicle is at the top of thedrawing, and is represented by 144. The load is carried by a plug member145, which fits a recessin the bottom of the vehicle and is preventedfrom turning by a hollow dowel 146, which is not in the plane of thesection.

Trapped beneath the outer assembly 143 is the cushion of air whichsupports the weight of the vehicle and provides resilience. The airpressure is of the order of 5 to 10 psi. The centre part of this cushionat 147 is more or less disc-shaped; the outer part is a hydrostaticbalance chamber 148. These two spaces freely intercommunicate. The spacebetween the periphery of the outer plug member and the cylindrical partof the primary seal, is closed by special flexible secondary seal Iassembly 149. When the vehicle is in motion, the air cushion space ispressurised hydrodynamically by the sliding of the primary seal ring onthe slipway. Pressure being generated by the same mechanism as that fora tilting pad thrust bearing. Excess air which is generated in this wayis released through a balanced nylon spool valve 150 to an exhaust belt151 which communicates with the atmosphere. When the vehicle is at restthe cushion is pressurised through an induction belt 152,

which is piped to a compressor discharge through the hollow dowel 146,the compressor being inside the vehicle. At intermediate speeds atransitory regime exists conducive to lubrication failure at thosesections of the sealing ring which are situated at specific known anglesfrom the leading centre line. In order to prevent this, should it'proveserious, hydrostatic pockets are provided, one of which is showndisplaced at 153. The primary seal assembly is free to advance, retreator tilt in relation to the plug member 145. Its surface loading, whereit bears upon the slipway, is governed by the projected area of thehydrostatic balance chamber 144. On initial pressurisation, scaling isensured by springs 154.

The primary seal assembly 143 comprises a plastics ring member, with aninternally machined cylindrical surface and a flat ring portion 157. Thebacking cushion 158, of plastics or rubber foam, allows the tire bearingsurface to accommodate small irregularities in the track surface 142. Aradial pressure gradient exists across the bearing surface of theprimary seal and the resultant tire load must be matched by uniformcompression of the backing cushion, without distortion of the matingsurface from a true plane.

In the secondary seal assembly 149, a ring of pure P.T.F.E. is preloadedby a chamfered loading ring and the compression springs 154 which areretained by a cage 162. The central plug assembly comprises the theequivalent spring stiffness depends on the plug interior volume with thedamping governed by the size of the passage 167. In an emergency thevehicle can start without the compressor operating, and to reduce trackscoring and starting friction a plug tyre 168 of P.T.F.E. is fitted. Toprevent this tyre drooping, a space behind it is vented by a radialgroove 169 and vent 170.

To refer again to FIG. 6, line A A A shows the axis of rotation of thewheel 43. Said wheel may be provided with a second pair of bearings,corresponding to the king-pin of an automobile, whereby the wheelbearings may pivot, about an axis B B B, causing the axis of rotation ofthe wheel so to pivot. By this means, caster action may be provided, toeliminate a source of wear which would otherwise be produced by thevertical bouncing of the vehicle, due to irregularities of the maintrack surface. Similarly, such caster action may be provided for thewheel 44, and, in order to eliminate corresponding wear due toirregularities in the curb members, wheels 41 may be provided withsimilar caster action, the axes of rotation being themselves pivotableabout axes B B, in each case. Similarly, with regard to FIG. 7, one axisA A, one axis B B and two axes C C are shown. These correspond to theaxes so named, in FIG. 6.

To refer again to FIG. 3, the wheels 12 may with advantage be placedinside members 14 and 16, as shown by 12. By this means, the wheels donot have to cross the grooves 15 and 17.

Referring now to FIG. 15, a hydrodynamic wedge is formed at 201 betweenthe primary seal and the slipway, by means of which the bearing isself-pressurised. Arrow 202 shows the direction of motion. An optionalduct 203 enables the bearing to be externally pressurised, by a pump orcompressor. This is of use for starting, and other circumstances whenthe self-pressurising mechanism is insufficient.

With reference to FIG. 16, the pocket 153 illustrates the application tothis embodiment of the principle shown in FIG. 14. If desired, a largepart, or the whole of tire surface 159 may be provided with dimples; thepocket 153 corresponds to a dimple of FIG. 14. In addition, if desired,the tyre surface 153 may be a disc, not a ring. That is to say, thecentral hole may be omitted, the whole area being constructed toresemble FIG. 14. The advantage of this latter modification is that,because the semi-compliant tire surface is in effect supported on aplurality of hydrostatic dimples, a crack in the surface of the slipwayor track, such as may normally be present at joints provided for thermalexpansion, will not rob the unit of an excessive proportion of itscarryingcapacity.

The limit flange 204 is rigidly joined, in this case, by an interferencefit to the primary seal. Excessive air, or liquid, causes the outwardlyprojecting flange of the plug member to engage this limit flange. Thiscauses the primary seal to be separated from the slipway surface,bleeding away excess air or liquid. This is an alternative or supplementto the valve 150. Its advantage is that it may limit, or accuratelylocate, the plug member, relative to the slipway, in a directionperpendicular to the slipway surface. To obtain location, without thevalve 150, an external flow restrictor may be fitted in the duct bywhich the bearing is externally pressurised.

With regard to the embodiments shown in FIGS. 15 and 16, it isemphasised that pressures are given only by way of example. In anyparticular case, pressures widely different from those described may beused. This is particularly the case should a liquid, such as oil orwater, be used instead of air. In this case, a means is provided, suchas a sprayer, to introduce the liquid to the leading edge of thebearing, or to pressurise it from an external pump. The advantage of aliquid is that pressures of a higher order may be used, withcorrespondingly increased carrying capacity.

FIG. 17 shows an embodiment wherein a vehicle 205 is supported by wheels206 above a track 207. Magnetic elements 208 and 209 are embedded in thetrack. Follower members are provided by vehicle-mounted sensingelements, which operate in pairs, 210, 211 on the guide member 208,and/or 212, 213, on the guide member 209.

FIG. 18 is a plan view of the embodiment shown in elevation in FIG. 1.Vehicle 1 rides track 3, as already described in this particular case;it is provided with two pairs of follower members, 5,5 and 7,7 whichoperate on the alternative guide members 4 and 6.

I claim:

1. Means of transportation comprising:

a. a vehicle,

b. a track having a selective branching zone and at least twoalternative branching routes,

c. two alternative guidance means for the vehicle,

d. each said guidance means comprising a stationary guide surfaceextending substantially continuously along the track through thebranching zone and parallel respectively to one of said branching.

routes,

e. one of said guidance means comprising an inwardly facing surfaceabove the level of the track and the other of said guidance meanscomprising an outwardly facing guide surface,

f. a vehicle-mounted primary follower associated with and engageablewith said inwardly facing guide surface, g

g. a vehicle-mounted secondary follower optionally engageable from abovewith and associated with said outwardly facing guide surface wherebysaid vehicle can be caused to select and follow that side of the branchcorresponding to said outwardly facing guide surface and thereby todisengage said primary follower from said inwardly facing guide surface,

h. said disengagement then taking place solely as a result of transversemovement of the vehicle away from said inwardly facing guide surface,and

i. alternative means by which said secondary follower can be moved clearof the outwardly facing guide surface thereby to cause the vehicle toselect and follow that side of the branch corresponding to said inwardlyfacing guide surface. s

2. Transportation means according to claim 1,

wherein the track is inclined transversely and in which said vehicle istransversely loaded by said transverse inclination of the track tomaintain effective contact with a selected one of said guide surfaces.

1. Means of transportation comprising: a. a vehicle, b. a track having aselective branching zone and at least two alternative branching routes,c. two alternative guidance means for the vehicle, d. each said guidancemeans comprising a stationary guide surface extending substantiallycontinuously along the track through the branching zone and parallelrespectively to one of said branching routes, e. one of said guidancemeans comprising an inwardly facing surface above the level of the trackand the other of said guidance means comprising an outwardly facingguide surface, f. a vehicle-mounted primary follower associated with andengageable with said inwardly facing guide surface, g. a vehicle-mountedsecondary follower optionally engageable from above with and associatedwith said outwardly facing guide surface whereby said vehicle can becaused to select and follow that side of the branch corresponding tosaid outwardly facing guide surface and thereby to disengage saidprimary follower from said inwardly facing guide surface, h. saiddisengagement then taking place solely as a result of transversemovement of the vehicle away from said inwardly facing guide surface,and i. alternative means by which said secondary follower can be movedclear of the outwardly facing guide surface thereby to cause the vehicleto select and follow that side of the branch corresponding to saidinwardly facing guide surface.
 2. Transportation means according toclaim 1, wherein the track is inclined transversely and in which saidvehicle is transversely loaded by said transverse inclination of thetrack to maintain effective contact with a selected one of said guidesurfaces.